Magnetic recording head



NOV. 25, 1947. QAMRAs 2,431,540

MAGNETIC RECORDING HEAD Filed March 2, 1945 mliililiiliiii 1,3

\ fizz En/Ur MARI 0v 69/12/46 by $44M mw figs Patented Nov. 25, 1947 MAGNETIC RECORDING HEAD Marvin Cami-as, Chicago, Ill., assignor to Armour Research Foundation, Chicago, 11]., a corporation of Illinois Application March 2, 1945, Serial No. 580,605

3 Claims. 1

This invention relates to a magnetic recording head and more particularly to a head which may be employed to magnetically record fluctuating electric energy on an elongated travelling record medium and to reproduce electrical fluctuations from a previously magnetized record medium.

One of the principal features and objects of the present invention is to provide a novel magnetic recording head which will provide exactly the same high quality of recording and reproduction which is obtained by using a head having the travelling record medium pass directly through the voice coil, but which employs, in this case, only an open slot.

It is one of the objects of the present invention to provide a novel sound head for a magnetic recording and reproducing device of the open slot type.

As the expression recording head is used throughout the description and claims of this case, it will be understood that it refers to a head for either making magnetic recordings on a travelling elongated record medium such, for example, as a magnetizable wire; or, for reproducing fluctuating electric energy corresponding to fluctuating energy which has previously been magnetical- 1y recorded on the travelling record medium.

A further object of the present invention is to provide a core piece of novel construction for a magnetic recording head.

Another and further object of the present invention is to provide a novel recording head in which the greater part of the recording head is at substantially zero M. M, F.

Another and still further object of the present invention is to provide a recording head having the electric recording or pick-up coil wound thereon ina novel manner.

Still another and further object of the present invention is to provide a novel method and means for magnetizing a traveling elongated record medium and for reproducing electric energy from a previously magnetized record medium.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, both as to its organization, manner of construction and method of operation, together with further objects and advantages thereof, may best be understood by reference to the accompanying drawing, in which:

Figure 1 is a front elevational view of the core ire-100.2)

a diagrammatic illustration of the flux pattern teachings of the present invention;

set up by the voice coil thereof.

Referring first to Figures 1 to 3 of the drawing, I have illustrated thereby one embodiment of the present invention. This embodiment of the present invention shows a core piece H, as shown in Figures land 2 of the drawing, which is formed of a single flat piece of magnetizable material. The material may be of any suitable composition having high magnetic permeability and low magnetic retentivity. By way of example and not byway of limitation, this core piece ll may be .020 in. in thickness, approximately in. long, and approximately /2 in. in height. The top edge is slightly curved as at l2 to provide a crown. This crowned edge I2 is grooved lengthwise as at l3 for receiving and confining a traveling elongated record mediumsuch, for example, as a wire it (see Figure 3).

A relatively large hole I5 is cut or punched in the center of the core member ll near the crowned edge l2, and in addition a slot (6 is out between the hole l5 and the upper crowned edge l2 of the core II. This slot I6 preferably is very narrow, such for example, as .002 in. If desired the slot may be filled with non-magnetizable material such, for example, as silver solder H, in order to maintain the spacing between the opposite sides of the slot at a uniform distance apart.

The metal of the core member II on the opposite sides of the slot l6 provides pole portions l8 and I9 when a magnetizing coil is wound on the core member H in a manner presently to be described.

In addition to the hole l5, two long narrow slots disposed substantially parallel to the crowned edge 12 are provided at 20 and 2|. These slots are placed as close to the edge l2 as is possible without causing the slots 20 and 2| to interfere or merge with the groove [3. The ends of the slots 2|] and 2| adjacent the pole pieces |8and ii! are spaced a substantial distance back from the pole tips for a reason which will hereinafter be explained. After the core member II is cut or punched in the manner described in connection with above description of Figures 1 and 2, a coil is wound therearound as shown in Figure 3. This coil is in the form of a continuous coil wound first through the slot 20 and the hole i and then through the slot 2| and the hole [5. The direction of winding of the coil through the slot 2| is the same as the direction of winding through the slot 20. This provides two coil portions 22 and 23, the outer ends 24 and 25 of which are arranged to be connected to the magnetic recorder apparatus. Th inner ends of the coil portions 22 and 23 are connected by the integral portion 25. In effect, the coil portions 22 and 23 are what would result from taking a single helically wound coil and breaking it open slightly in the middle. If, for example, at an instant of time when the current is flowing up through the conductor 24 and down through the conductor 25, the left-hand end of the coil portion 22 will be a south pole and the right-hand end thereof will be a north pole. Furthermore, the left-hand end of the coil portion 23 will be a south pole, and the right-hand end of the coil portion 23 will be a north pole. We thus see that there is a very strong concentration of flux across the gap l6 sinc the two inner ends of the coil portions 22 and 23 ar of opposite polarity. Due to the fact that there is a large amount of magnetizable material below the coil portions 22 and 23, the return fiux path is predominantly concentrated in that region. A small amount of flux path returns above the top portion of the coil portions 22 and 23adjacent the groove i3. Since there is only a very small amount of metal here due to the fact that the slots 20 and 2| were close to the top edge of the core member II, it will be readily appreciated that the flux carried in this region is very small.

In order to compare the difference between a coil wound in the manner above described with an open slot type recorder head of the prior art, such a prior art construction has been illustrated in Figure 4 of the drawing. More particularly, the core member ii and the prior art structure have a magnetizing and pick-up coil 21 wound through the central hole i5 and over the bottom edge 28 of the core member ll. Let us now compare the difierence. Assuming that the magnetizing field force at one end of the coil 21 is plus ten and that the other end is minus ten, we then find that the field at th upper left-hand corner of the core member may be minus nine and at the upper right-hand corner plus nine units of field force. Across th gap 16, we have minus seven units at one pole and plus seven at the other pole. Due to the fact that there is a difference of M. M. F. at the opposit corners of the core member, there is a large leakage field as shown by the flux lines in Figure 4. This field is spaced around the core member II and introduces distortion into the wire when a recording is made.

In Figure 3 of the drawings, let us assume that the units of M. M. F. are the same at the pole tom and end edges of the core member Ii are all at zero magnetic potential. This is true even of the upper corners of the-core member II. The most important thing is that the greatest magnetic potential is right at the air gap and that it rapidly decreases along the upper edges in opposit direction as distinct from the prior art open slot type of recording head wherein the magnetic potential increases (in a postive or negative direction) as you move away from the air gap along the upper edge of the core member. The result of the construction shown in Figure 3 is that substantially the sam result and the same effect is obtained as though the wire were passed directly through the center of the magnetizing coil. This latter type of arrangement has the great advantage of giving a much higher fidelity but has the disadvantage of not being able to readily insert and remove the wire from the recording head. The construction described herein has the advantages of both prior art types of heads and neither of the disadvantages of the prior art types of heads. Namely, it has the advantage of giving a, high fidelity of a closed type head and yet at the same time has the advantage of providing an open slot head in which the wire may be introduced and removed even though the ends of the wire are confined.

The impedance of the recording head may be varied by varying the number of turns of wire in the coil portions 22 and 23 and the windings may be in the form of a single layer or a plurality of layers depending upon the impedance desired.

While I have shown a particular embodiment of my invention, it will, of course, be understood that I do not wish to be limited thereto, since many modifications may be made, and I, therefore, contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

I claim as my invention:

1. A magnetic recording head comprising a plate of relatively high magnetic permeability and relatively low magnetic retentivity, a groove extending alon one edge of said plate for receiving and guiding a traveling record medium, said plate having a non-magnetic gap therein extending' inwardly from said one edge, said plate having a pair of slots in close proximity to said one edge on opposite sides of said gap, said plate having at least one additional opening therein, and a magnetizing coil wound through said slots and said additional opening.

2. A magnetic recording head comprising a plate of relatively high magnetic permeability and relatively low magnetic retentivity, a groove extending along one edge of said plate for receiving and guiding a traveling record medium, said plate having a non-magnetic gap therein extending inwardly from said one edge, said plate having a pair of slots in close proximity to said one edge on opposite sides of said gap, said plate having at least one additional opening therein, and a magnetizing coil wound through said slots and said additional opening, the cell being wound the same way on both sides of said gap, whereby the adjacent ends of the coil portions on opposite sides of said gap are of opposite magnetic polarity.

3. A magnetic recording and reproducing head comprising a core member of relatively high magnetic permeability and relatively low magnetic retentivity, means for guiding a traveling record medium over a predetermined path, at least three apertures in said core member, the first and sec- 0nd of said apertures being located in close proximity to said path of travel of said record medium, said core member having a non-magnetic gap between said first and second apertures, and a recording and reproducing coil wound partly through the first and partly through the second of said apertures and the additional apertures.

file of this patent:

UNITED STATES PATENTS Number Name Date MARV CAMRAS, 2,351,007 Camras June 13, 1944 REFERENCES CITED FOREIGN PAIEMS Number Country Date The following references are of record in the 357,378 Great Britain Sept. 14,1931 805,434 France Nov. 19, 1946 

